A fired up and angry Donkey Kong champ has let loose on the witness box, describing why he is suing a Brisbane YouTuber over a “heinous” video he alleges gave rise to an imputation he hounded a young man to his death.

Donkey Kong arcade champion Billy Mitchell vomited after he watched a YouTuber's video linking him to a young man's death, a judge has heard.

Concerns about a famous American arcade gamer using his phone inside a courtroom during a defamation trial have been raised by a judge.